Inspection of solder ball or solder joints is crucial in achieving high quality non-defective circuit boards. In particular, with the trend towards the use of surface mounted components, the importance of determining whether an effective amount of solder and flux is applied to the solder joint before the components are mounted becomes even more critical. To avoid an unacceptable yield and having to rework or scrap the printed circuit board, the soldering process is periodically monitored by visual inspection. If an insufficient amount of solder or flux exists, the likelihood of circuit board (or module) failure becomes certain. Thus, existing vision systems attempt to determine whether an effective amount of solder and/or flux exists. Unfortunately, to the human eye, the conventional inspections of solder joints in two-dimensions may provide a false conclusion as to the effectiveness of the solder joint or flux or even the existence of the solder joint itself. Furthermore, to the human eye, flux appears clear when applied to a printed circuit board. Thereby providing further room for error during visual inspection.
When conventional vision inspection systems use white light (incandescent or fluorescent) to inspect a joint, the two dimensional view of a solder joint having an insufficient amount of solder or flux may still appear as if it were sufficient. Thus, present vision schemes are ineffective in accurately determining the efficacy of a solder joint. Other vision systems may use dyes to enhance the inspection when using white light. Unfortunately, the dye may cause dendritic growth or corrosion in the solder joint.
Having an appropriate amount of flux on the under side of an integrated circuit (as in the C-5 Process for Chip Carriers) is required to act as an activator during reflow and to provide a tacking media during transportation. Too much flux causes the integrated circuit to float away when the flux liquifies. An insufficient amount of flux fails to provide enough tackiness during transportation. A need exists for a method to accurately determine the effectiveness of a solder joint and the added flux before surface mounted components are mounted that does not necessarily require additional production steps.